Due to the advance of electronic technology, especially for the popularity of portable electronic products, the requirements of light, compact and low-energy consuming display devices are gradually increasing. With the advantages of low-energy consuming, low-heat dissipation, light weight and non-luminescence, liquid crystal display (LCD) device have been widely used in the electronic products and even have replaced the traditional CRT display device.
Referring to FIG. 1, it depicts a conventional LCD device. Typically, the LCD device 10 includes a liquid crystal display (LCD) panel 12 and a backlight module 14. The backlight module 14 is disposed under the LCD panel 12 for distributing the lights from a light source uniformly over the surface of the LCD panel 12. The LCD device 10 further includes a frame 16 for mounting the LCD panel 12 and the backlight module 14.
The refractive indexes of major axis and minor axis of a liquid crystal (LC) molecule in the LCD panel 12 are different, and thus an image depends on the viewing angle of a viewer when the viewer watches the screen of the LCD panel 12. When the viewing angle is gradually big, the contrast is decreased, the color is changed, and even the gray scale is reversed. According to those disadvantages, various types of wide viewing angle technique are developed so as to solve the above-mentioned problem.
Recently, a multi-domain vertical alignment (MVA) technique and a transverse electric field technique are mainly two types of wide viewing angle technique. A fringe field switching (FFS) technique belongs to the transverse electric field technique. The FFS technique has high transmission, wide viewing angle, low color contrast, etc., and thus the FFS technique is one of potential techniques.
Referring to FIGS. 2 and 3, they depict an array substrate 30 of a conventional FFS type LCD panel. A first metallic layer is formed on a glass substrate 32, and is patterned to a plurality of gate lines 34. A plurality of common electrodes 36 are disposed on the glass substrate 32, and the common electrodes 36 and the gate lines 34 are located on the same level. A gate insulating layer 38 is disposed on the glass substrate 32, and covers the gate lines 34 and the common electrodes 36. A second metallic layer is formed on the gate insulating layer 38, and is patterned to a plurality of data lines 40, source electrodes 42 and drain electrodes 44. A passivation layer 46 is disposed on the gate insulating layer 38 and covers the data lines 40, the source electrodes 42 and the drain electrodes 44. A plurality of pixel electrodes 48 are disposed on the passivation layer 46, wherein the pixel electrodes 48 is electrically connected to the drain electrodes 44 by a through hole 50.
Referring to FIG. 4, recently the conventional FFS type LCD panel 12 is characterized in that a layer of transparent electrode 36 (i.e. the common electrode 36 shown in FIG. 3) is added on the bottom of a lower substrate 20 (i.e. the array substrate 30 shown in FIG. 3). The pixel electrodes 48 and the common electrodes 36 can be acted as upper and lower electrodes respectively so as to form a transverse electric field. The transverse electric field can control the rotation of LC molecules 26 in an LC layer 24 between the upper and lower substrates 22, 20.
However, the pixel electrodes must be electrically connected to the drain electrodes by the through hole. The through hole can decrease the aperture ratio of a pixel. Furthermore, when the common electrodes are designed, the distance between the common electrode and the gate electrode must be not small so as not to increase the aperture ratio of a pixel. In addition, the disclination phenomenon of the LC molecules is that the LC molecules are non-continuously arranged in the rubbing direction. The area caused by disclination lines must be considered, and thus useful aperture ratio of a pixel is lower actually. According to the LCD panel with middle size and small size, low aperture ratio of the LCD panel can increase the cost of the backlight module in order to meet the requirement of standard brightness. Thus, lately the low aperture ratio is a disadvantage when LCD panel maker competes with other maker in the market of the LCD panel with middle size and small size.
Accordingly, there exists a need for an array substrate for FFS type LCD panel capable of solving the above-mentioned problems.